Exercise 17. Concurrency terms

1. Thread Synchronisation - Thread synchronization requires that a running thread gain a "lock" on an object before it can access it. The thread will wait in line for another thread that is using the method/data member to be done with it. This is very important to prevent the corruption of program data if multiple threads will be accessing the same data. If two threads try to change a variable or execute the same method at the same, this can cause serious and difficult to find problems. Thread synchronization helps prevent this.

2. Locks - In computer science, a lock is a synchronization mechanism for enforcing limits on access to a resource in an environment where there are many threads of execution. Locks are one way of enforcing concurrency control policies.

3. Deadlock - Deadlock most often occurs when two (or more) threads are each waiting for the other(s) to do something.

4. Semaphores - a semaphore is a protected variable or abstract data type which constitutes the classic method for restricting access to shared resources such as shared memory in a multiprogramming environment. A counting semaphore is a counter for a set of available resources, rather than a locked/unlocked flag of a single resource.


5. Mutex (mutual exclusion) -Mutual exclusion (often abbreviated to mutex) algorithms are used in concurrent programming to avoid the simultaneous use of a common resource, such as a global variable, by pieces of computer code called critical sections.

Examples of such resources are fine-grained flags, counters or queues, used to communicate between code that runs concurrently, such as an application and its interrupt handlers. The problem is acute because a thread can be stopped or started at any time.

6. Thread - a thread of execution results from a fork of a computer program into two or more concurrently running tasks. The implementation of threads and processes differs from one operating system to another, but in most cases, a thread is contained inside a process. Multiple threads can exist within the same process and share resources such as memory, while different processes do not share these resources.

7. Event - event-driven programming or event-based programming is a programming paradigm in which the flow of the program is determined by events — i.e., sensor outputs or user actions (mouse clicks, key presses) or messages from other programs or threads.

Event-driven programming can also be defined as an application architecture technique in which the application has a main loop which is clearly divided down to two sections: the first is event selection (or event detection), and the second is event handling. In embedded systems the same may be achieved using interrupts instead of a constantly running main loop; in that case the former portion of the architecture resides completely in hardware.

8. Waitable Timer - A waitable timer object is a synchronization object whose state is set to signaled when the specified due time arrives. There are two types of waitable timers that can be created: manual-reset and synchronization. A timer of either type can also be a periodic timer.